WO 95/33006 published Dec. 7, 1995 relates to a thermoplastic elastomer blend comprising 50% to 99% by weight of at least one styrenic block copolymer and 1% to 50% by weight of at least one homogeneously branched ethylene interpolymer having a density from 0.855 g/cc to 0.905 g/cc wherein the ethylene interpolymer in the amount employed is a substantially inert extender characterized by certain properties. Exemplified are compositions containing certain S-I-S species as well as a mixture of Kraton G-1650 and Engage 8100 at weight ratios of 1:3 to 3:1.
The present invention is a hot melt adhesive composition comprising at least one homogeneous ethylene/xcex1-olefin interpolymer which is an interpolymer of ethylene and at least one C3-C20 xcex1-olefin and at least one block copolymer. Preferably, the concentration of the homogeneous ethylene/xcex1-olefin interpolymer ranges from about 5 wt-% to about 40 wt-%, whereas the concentration of the block copolymer ranges from about 1 wt-% to about 40 wt-%, more preferably from about 10 wt-% to about 20 wt-%. The adhesive composition further comprises at least one additional hot melt adhesive ingredient including tackifiers, plasticizers and waxes. In the case of pressure sensitive adhesives, at least one tackifying resin and a plasticizing oil are preferred, whereas for non-pressure sensitive adhesive compositions at least one tackifying resin and at least one wax is preferred. The tackifier is preferably employed at a concentration of at least about 30 wt-%.
The homogeneous ethylene/xcex1-olefin interpolymer preferably has a density ranging from 0.850 to about 0.885 g/cm3. To minimize the molten viscosity of the adhesive composition, the homogeneous ethylene/xcex1-olefin interpolymer preferably has a melt index of greater than about 10 grams/10 minutes, more preferably greater than about 30 g/10 minutes, even more preferably greater than about 100 g/10 minutes, and most preferably greater than about 500 g/10 minutes.
The block copolymer is preferably a hydrogenated block copolymer having non-elastomeric end-blocks of styrene and a rubbery mid-block of ethylene/propylene, ethylene/butylene or mixtures thereof. For low viscosity adhesive compositions, preferably the block copolymer has a solution viscosity of less than about 5000 cps for a 25 wt-% solution of block copolymer. Further, for increased cohesive strength, the block copolymer preferably contains a minimal amount of diblock ranging from 0 wt-% to about 20 wt-%. For high performance pressure sensitive adhesives, preferably a saturated block copolymer having a high vinyl content midblock is employed.
The adhesive compositions are useful for a variety of end-use hot melt pressure sensitive adhesive applications including removable grades, semi-permanent and permanent grades, as well as freezer grade adhesive compositions. The inventive pressure sensitive adhesive compositions exhibit good heat resistance, enhanced non-staining characteristics and reduced residual transfer tendencies. These compositions also exhibit superior adhesion and superior resistance to ultraviolet (UV) light. Accordingly, the compositions are well suited for a variety of tape and label applications, particularly those having paper substrate backings, as well as positioning adhesives for feminine napkins. Due to the heat and UV light resistance, the adhesive compositions also find utility in a variety of xe2x80x9chigh performancexe2x80x9d tape and label applications including packaging tapes, tape applications for automobiles, carpet tapes, xe2x80x9chook and loopxe2x80x9d applications (Velcro(copyright)), labels for windows (automobile, boat and construction industries), labels for appliances and electronics, shelf marking adhesives and so forth. The novel pressure sensitive adhesives may also be utilized for bookbinding applications including lining-up, tightbacking, book joint, side glue, puzzle and gameboard lamination, thread-securing or gluing-off, facing and slip cases. Such applications however, may also employ non-pressure sensitive adhesives.
The inventive non-pressure sensitive adhesive compositions find particular utility in paper packaging and bookbinding applications such as one shot or perfect bookbinding, two shot bookbinding, Rep-Kover, casing-in and casemaking. In the case of low temperature applied hot melts, both the set temperature and the heat resistance is substantially improved, whereas in the case of bookbinding adhesive, the composition exhibits enhanced tensile strength in combination with improved heat resistance while maintaining a low molten viscosity.